Accessing multiple Fields in a matlab struct

Question

I am trying to acces multiple fields in an struct to change the data from datenum to datetime. The struct is created by:

    DATA=struct('Id',[],'Date',[],'Value',[]);

and due to the style of receiving the Data, there are multiple DATA with each having one Value. So a sufficent example would be

    Data(1).Date=2;
    Data(2).Date=3;

now i would like to change the entry to datetime but leaving the data structure as it is. FOr the example lets say to square the date to.

    Data(1).Date=4;
    Data(2).Date=9;

The struct has about 50000 enries and arrayfun() does not give an efficient enough solution. I cant find a way to convert the entire array of Data.Date ad once deal() write all 50000 dates in each field and in every other way i receive errors. Does someone has a solution to change the entire array and write it back in each Field of the array?

Tim Adams · Accepted Answer · 2015-12-13 16:16:28Z

3

You could put all of the values into an array and then repopulate the structure after calculating the results.

arr=[Data(:).Date];
arr=arr.^2;
for a=1:numel(arr)
   Data(a).Date=arr(a);
end

answered Dec 13, 2015 at 16:16

Tim Adams

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2 Comments

Finn Over a year ago

It is way better than the arrayfun() (~3seconds to ~30 seconds), but i would like to avoid for loops, as there might be a way to handle this as array. neverless Thank You, i will take this solution if no other is possible

Tim Adams Over a year ago

You might be able to try doing something like [Data(:).Date]=arr, but I don't have a copy of Matlab to verify this with.

Daniel · Accepted Answer · 2015-12-13 16:28:50Z

2

Using a small detour converting form struct to array, then do the math, then convert from array to cell to comma separated list to a struct:

arr=[Data(:).Date];
arr=num2cell(arr.^2);
[Data(:).Date]=arr{:};

answered Dec 13, 2015 at 16:28

Daniel

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1 Comment

Finn Over a year ago

Thank you, well this is just swell. I checked the performance of both given solutions against my old arrayfun approach. for who is intrested on performing datetime on 50000 entries: arrayfun - 23sec for loop - 3.3sec num2cell - 3.3sec both solution appear to have the same performance but i am going to stick to the num2cell as, as mentioned, i would like to avoid loops in the code. Again Thank you both

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